Method of purging and washing solids in a centrifugal



March 28, 1939. c A, QL'CQTT 2,152,562

METHOD OF PURGING AND WASHING SOLIDS IN A CENTRIFUGAL Filed June 27, 1935 a E i i AAAAA A AAMUAAAA l6 g INVENTOR P QHARLES A. OLCOTT 2 BY HIS ATTORNEYS Patented Mar. 28, 1939 UNITED STATES PATENT OFFICE METHOD OF PURGING AND WASHING SOLIDS IN A CENTRIFUGAL This invention relates to the separation of solids from liquors in which they are contained and more particularly to the separation and washing of solids in a centrifugal dryer and it 5 is an object of this invention to provide an improved method of separating such solids from the liquors in which they are contained, washing the solids to remove retained traces of the containing liquors and removing the wash liquid Without drying the solids to such an extent that they are hard and difiicult to remove from the dryer. It is also an object of this invention to provide an improved means for carrying out the method.

In the drawing Fig. 1 is a substantially diagrammatic vertical section of a centrifugal dryer for preparing ma- .terials in accordance with this invention;

Fig. 2 is a view taken as a section on the line 80 2--2 of Fig. 4, showing in substantially diagrammatic form a means used in controlling the separator of Fig. l in carrying out this invention;

Fig. 3 is a front view of the dial shown in Fig.

35 Fig. 4 is a partial side'view of the control means shown in Fig. 2. I

In the following description, for the purposes of illustration, the method is set forth as applied to the separation of sugar from its mother liquor 30 but it is to be understood that the method is not limited in its operation to the separation of such solid only as it can be used in the separation of other solids such as salt, borax and other similar solids similarly separated from the con- 35 taining liquors.

In the production of sugar, a centrifugal dryer is used to remove the mother liquor or molasses from the sugar. The centrifugal force, to a great extent, overcomes the tendency of the molasses 40 to adhere to the sugar crystals but, regardless of the speed of rotation of the dryer some mo-, lasses adheres in the form of a film on the crystals. To remove the molasses film from the sugar crystals the sugar is washed by spraying with 46 a suitable washing liquid, as water or a syrup,

while still in the rotating dryer. In this washing step, the washing liquid removes the molasses film from the crystals leaving a substantially pure sugar, and it also dissolves a certain amount 50 of the sugar so that it is desirable to efiect the washing with the use of the smallest possible quantity of the washing liquid in order to keep down the expense of recovering the sugar from the washing liquid. After the washing is com- 55 pleted the rotation of the dryer is continued to remove as much as possible of the washing liquid,.but the sugar crystals' retain a film which is substantially a pure solution of sugar in water. This film coats the crystals and if the rotation of the dryer is carried to the point where air is passed between the crystals sufficiently to dry the film, the sugar of this film is recrystallized and serves to cement the sugar crystals into a mass which is removed from the dryer only with considerable difficulty.

While a highrotative speed is desirable for separating the mother liquor from the sugar because of the more nearly complete removal of the mother liquor efiected thereby and the smaller quantity of washing liquid required to remove what remains, it has not previously been used, however, because of the impossibility of stopping the rotation of the dryer before the air passing" between the crystals dries the film left upon removal of the washing liquid and cements the crystals in the dryer into substantially a. solid mass. To overcome these objections the removal I of the mother liquor and the washing of the sugar at a lower speed, that is, a speed low enough to prevent the recrystallization of the sugar in the washing liquid retained by the sugar and the bonding together of the sugar crystals thereby. In its practical application the separation of the 5 mother liquor or molasses from the sugar is carried out with the basket of the dryer rotatingat about 1200 R. P. M. Upon completion of the removal of the molasses the speed of rotation of the basket is decreased gradually to about 950 R. P. M. and while the speed of the basket is decreasing the washing liquid is' applied, the period required for the reduction of the speed of the basket being made sufiiciently long to permit of the desired amount-of washing liquid being ap- 4 plied; so that the basket attains the desired reduced speed at the time, or immediately after, the supply of washing fluid is cut off. During the time the washing liquid'is being drawn oil.

the speed of rotation of the basket is further rebe by any usual and suitable means which admit justable resistance 20.

of the basket being operated at the desired speeds for the proper lengths of time.

In the drawing, however, for the purpose of illustration the basket I of the dryer is shown operated by a two-speed motor 2 through a centrifugal clutch 3 and shaft 4 as in the patent to Mackintosh, No. 15,115, reissued May 31, 1921. Washing liquid may be supplied to the basket I through the nozzle 4 and pipe 5 from a suitable source of supply, the liquid being supplied under constant pressure for definite periods of time, and the supply of the liquid may be controlled by any suitable means as, for example, the controlling means shown in the patent to Steps, No. 1,947,679, Feb. 20, 1934, or the patent to Roberts, 1,224,095, April 24, 1917.

The motor 2 may be of any suitable type and arranged for operation on either an alternating or a direct current circuit. Inthe drawing the motor is shown as of the induction or slip ring type operable on an alternating current circuit with connections from the rotor 8, through slip rings 8 and II, leads I! and I4, fixed contact l8,

and movable contact I! to complete a circuit of variable resistance through resistance 20. In a motor of the type described varying the current in the rotor varies the tendency of the rotor to rotate with the field produced by the alternating current in the stator and provides a means for controlled regenerative braking in reducing the speed of rotation of the dryer from the high speed at which the mother liquor or molasses isremoved to the lower speeds at which the sugar is washed, the washing liquid removed and the sugar broken up for removal from the basket. When the motor controller, not shown, is operated to change the operation of the motor from its higher to its lower speed, that is, from a speed of 1200 R. P. M. to 600 R. P. M. the momentum of the basket I serves to drive the rotor 8 as a generator, the load thereon and the resulting braking effect being determined by the resistance of the circuit including the ad- Where the time during which the washing liquid is supplied is controlled, as in the Steps patent previously referred to, the shaft 22 which operates the movable contact l8 may be the shaft in the Steps construction which serves to operate the means for varying the time during which the washing liquid is supplied. Where this arrangement is used, as in Fig. 4, the resistance in the rotor circuit is arranged so that when the shaft 22 is operated to lengthen the time during which the washing liquid is supplied, the movable contact II is shifted to increase the reslstance in circuit with the rotor 6, reducing the current in the rotor and the braking eflect therefrom and decreasing the rate of deceleration of the rotor and basket, the resistance-being so proportioned that the speed of the dryer will decrease from the speed at which the mother liquor is removed to the speed at which the washing liquid is removed in a slightly longer period than is required for supplying the washing liquid. Operating the shaft 22 in the opposite direction to decrease the time during which the washing liquid is suppliedwill operate the movable contact ll to decrease the resistance in the rotor circuit and increase the rate of deceleration of the rotor but the time required to reduce the speed of rotation of the dryer to the speed at which the washing liquid is removed is always slightly in excess of the time during which the washing liquid is supplied. While the resistance 20 is described as being regulated by the shaft which regulates the time during which washing liquid is supplied, it is to be understood that separate shafts independently operated may be used and while the motor 2 is described as being an alternating current motor it is to be understood that a direct current motor could be regulated in the same manner.

In Fig. 1 there is shown diagrammatically the wiring for operating the motor 2, at high and low speeds as an alternating current motor, a single phase only of the alternating current circuit being shown. Current is supplied from ,a source of power by the leads L and L to a double throw switch 25 which in one position connects the source of power through leads 2! and 28 to the high speed winding 26 and in the other position connects the source of power through leads ll and 32 to the low speed winding 30. The switch 25 is also provided with contacts which complete a. shunt through leads 34 and 35 around the re sistance 20 when the source of power is connected to the high speed winding 26 but which contacts leave the shunt open when the source of power is connected to the low speed winding 30.

Whatis claimed is:

1. In a process of separating solids from a containing liquor the steps of centrifuging the liquor from the solids at a high speed of rotation and treating the solids with a washing liquid while decreasing the speed of rotation from the high speed to a predetermined lower speed.

2. In a. process of separating solids from a containing liquor the steps of centrifuging the liquor from the solids at a high speed of rotation, treating the solids with a washing liquid while decreasing the speed of rotation to a. predetermined lower speed and centrifuging the washing liquid from the solids at a lower speed.

3. In a process of separating solids from 9. containing liquor the steps of centrifuging liquor from the solids at a high speed of rotation, treating the solids with a washing liquid while decreasing the speed of rotation and centrifuging the washing liquid from the solids while further decreasing the speed.

4. In a. process of separating solids from a containing liquor the steps of centrifuging the liquor from the solids at a constant high speed, washing the separated solids while centrifuging at a. lower speed and completing the centrifuging of the washing liquid from the material at a still lower speed.

5. In a process of separating sugar crystals from 9. containing liquor, the steps of centrifuging the liquor from the solids at a high speed of rotation, treating the solids with a washing liquid, and decreasing the speed of rotation during the washing period to a speed, less than that at which the air currents dry and cement the crystals.

6. In a process of separating sugar crystals from a containing liquor, the steps of centrifuging the liquor from the solids at a high speed of rotation, treating the solids with a washing liquid, decreasing the speed of rotation during the washing period to a speed less than that at which the air currents dry and cement the crystals and centrifuging the washing liquid from the crystals at a still lower speed.

7. The combination with a centrifugal dryer of means for rotating said dryer at predetermined different speeds, means for supplying a predetermined amount of washing liquid to the dryer in a predetermined period, braking means for providing a predetermined deceleration of the dryer from its higher operating speed during the period in which the washing liquid is supplied and means connecting said liquid supplying means and braking means for simultaneously adjusting the rate of deceleration of the dryer in accordance with changes in the period during which liquid is supplied.

8. The combination with a centrifugal dryer of means for operating said dryer at a plurality of predetermined speeds, means for supplying a predetermined amount of washing liquid to the dryer in a predetermined period, braking means for reducing the speed of the dryer from its 9. "I'he combination with a centrifugal dryer' of means for rotating said dryer at a high speed for purging the basket contents of the mothera liquor and a low speed for discharging the basket means connecting said liquid supplying means and braking means for simultaneous adjustment thereof. a

10. The combination with a centrifugal dryer of means for rotating said dryer at a high speed for purging the basket contents of the mother liquor and a low speed for discharging the basket contents, means for supplying a predetermined amount of washing liquid to the dryer in a predetermined period, braking means for reducing the speed of the dryer during the washing period from its high speed to a speed less than the speed at which the contents of the basket cement and means connecting said liquid supplying means and braking means for simultaneously increas ing the volume of the washing liquid and lengthening the period required for speed reduction.

11. The combination with a centrifugal dryer of means for rotating said dryer at different speeds, means for supplying washing liquid to the dryer for a predetermined period, braking means for reducing the speed of the dryer from its higher speed to a predetermined speed intermediate said diiierent speeds in the washing period and means connecting said liquid supplying means and braking means for simultaneously adjust ing the washing period and the deceleration of the dryer.

12. The, combination with a centrifugal dryer of an induction motor for operating said dryer at different speeds, means for supplying washing liquid to the dryer for a predetermined period, means for including an electrical resistance in the circuit of said rotor for eifecting a predetermined speed reduction in the washing period and means for simultaneously varying the washing period and said resistance for maintaining the relation of speed reduction period to the washing period.

13. The combination with a centrifugal dryer of an induction motor for operating said dryer at difierent speeds, means for supplying a pre-- determined volume of washing liquid to the dryer, regenerative braking means for reducing the speed of rotation of the dryer from the higher speed to a predetermined speed in the washing period and means for simultaneously varying the volume of washing liquid supplied and the speed reduction period, CHARLES A. OLCOTI. 

